I'd really like to see Patrum Scuta be made compatible with CK2+; the COA (especially the pagan ones) are so much better than the ones in vanilla/CK2+, and I'd love to be able to play with both.
Also, this is probably very unlikely and, if not, definitely very ambitious, but I'd love to see a compatibility patch between CK2+ and Tianxia: Silk Road Expansion. Granted, it would probably at least need to wait for the mod to get into Open Beta (though it would probably be best to wait until the actual release), but I'd love to be able to play in East Asia while using CK2+. Obviously, though, I'm not getting my hopes up for this, as it will probably never happen, seeing how both mods have major additions to CK2.